1. Field of the Invention
The present invention relates to a sheet aligning apparatus that aligns sheet-like recording media (hereinafter, “sheets”) carried thereto such as recording paper and overhead projector (OHP) sheets; a sheet processing apparatus that includes the sheet aligning apparatus and performs predetermined processing such as sorting, stacking, binding, folding, and punching to the sheets; and an image forming apparatus that integrally or separately includes the sheet processing apparatus.
2. Description of the Related Art
A sheet post-processing apparatus performs post-processing in, for example, the following steps. That is, sequentially receiving sheets from an image forming apparatus; aligning the sheets into a sheet bundle composed of a plurality of sheets; and automatically binding, or aligning punched sheets as the sheet bundle and sorting the bundle per unit. The post-processing apparatus is a so-called finisher. Although such a sheet post-processing apparatus can handle various types of sheets, if the sheets are soft sheets (paper) or curled sheets, the sheets cannot be surely moved by pressing of a wall surface of an aligning unit.
FIGS. 31A, 31B, and 31C are exemplary diagrams of a conventional general sheet aligning apparatus. FIG. 31A is a diagram of a state where a sheet Sn (an uppermost paper) is newly discharged on a sheet bundle S on an alignment tray 600. Assume that as shown in FIG. 31A, both ends of the sheet Sn are curled. In this state, when a movable jogger 602 moves and presses an end of the sheet Sn, an edge surface a of the sheet slides up as illustrated in FIG. 31B. Thus, when the jogger 102 moves further and reaches the side surface of the sheet bundle S, the sheet Sn does not move therealong. When the jogger 102 returns to its home position as illustrated in FIG. 31C, the edge surface a returns to the state of FIG. 31A. Thus, the sheet Sn is unmoved, and therefore, the sheet is not aligned. This happens not only when the sheet is curled but also when the sheet is soft. When the jogger presses the end of the soft sheet, the end of the sheet gets buckled and thus the sheet is not moved. The sheet may be moved for a small distance before buckling but in that case, the sheet is aligned only by the small distance before buckling, resulting in an incomplete alignment.
The edge surface refers to a cut surface sheet bundle that is formed when a large size sheet bundle is cut to create a small size sheet bundle. The edge surface a corresponds to an end in the longitudinal direction of the sheet and a side in the lateral direction. In this specification, the edge surface is referred to as an end or a side.
A sheet processing apparatus for processing sheets of curled paper and soft paper is disclosed in, for example, Japanese Patent Application Laid-open No. 6-016318 or Japanese Patent No. 3648073.
Japanese Patent Application Laid-open No. 6-016318 discloses a sheet processing apparatus that includes a sheet mounting unit and a pair of sheet side regulation side plates provided on both sides of the sheet on the sheet mounting unit. The sheet mounting unit stores therein or discharges and stacks thereon the sheets. At least one of the sheet side regulation side plates is movable in directions of narrowing and widening the distance to another plate. With the movement, the sheet on the sheet mounting unit is moved to be positioned between the plates, whereby the sheet is aligned. At a contact surface of the sheet side regulation side plate contacting a side end of the sheet in the post-processing apparatus, the friction to the sheet is made to be small in a direction from up to down and to be large in a direction from down to up. As a result, the curled sheet can be appropriately aligned. To provide the large friction, hair implantation sloping downward or saw-toothed concavity and convexity forming are performed.
Japanese Patent No. 3648073 discloses a sheet processing apparatus that teaches processing a holding surface of a pusher mechanism holding the lower end of the sheet so that the lower end of the sheet easily moves in the sheet pressed direction but does not easily return in the opposite direction, thereby preventing the pressed and aligned sheet from moving on the holding surface of the pusher mechanism.
The conventional techniques prevent the edge surface of the sheet from sliding to align the sheet by forming concavity and convexity on the wall surface of the jogger or adjusting a hair implant direction. However, the alignment accuracy of the jogger is affected by the concavity and convexity as a shape of the wall surface or due to hair implantation, and concavity and convexity along the concavity and the convexity are generated on the side surface of the aligned sheet bundle. As a result, the sheet cannot be accurately aligned unlike counterparts aligned by a planer wall surface.